This paper presents three curious findings about deterministic public-key encryption (D-PKE) that further our understanding of its security, in particular because of the contrast with standard, randomized public-key encryption (R-PKE):

(1) It would appear to be a triviality, for any primitive, that security in the standard model implies security in the random-oracle model, and it is certainly true, and easily proven, for R-PKE. For D-PKE it is not clear and depends on details of the definition. In particular we can show it in the non-uniform case but not in the uniform case.

(2) The power of selective-opening attacks (SOA) comes from an adversary\'s ability, upon corrupting a sender, to learn not just the message but also the coins used for encryption. For R-PKE, security is achievable. For D-PKE, where there are no coins, one\'s first impression may be that SOAs are vacuous and security should be easily achievable. We show instead that SOA-security is impossible, meaning no D-PKE scheme can achieve it.

(3) For R-PKE, single-user security implies multi-user security, but we show that there are D-PKE schemes secure for a single user and insecure with two users.

This article proposes a method for the construction of a public key system that is based on VLSI logic synthesis algorithms. First, we discuss the properties of VLSI logic synthesis algorithms. Then we view them in the context of cryptographic primitives. Then we propose a public key encryption system and finally discuss its security properties.

In 2014, Lin proposed an authentication system with dynamic identity of the user for low-power mobile devices using Chebyshev chaotic map. The scheme is proposed to provide mutual authentication and session key agreement between a remote server and its legitimate user. The scheme provides user anonymity and untracibility, and resilience from many cryptographic attacks. However, the author of this paper showed that Lin\'s scheme is no longer usable for practical applications as (i) it cannot verify the wrong identity and password at the user side in the login and password change phases, (ii) it cannot protect user impersonation attack, and (ii) it has the problem of session key forward secrecy.

For many cryptographic primitives and in particular for correlation-secure hash functions all known constructions are in the random-oracle model. Indeed, recent negative results by Wichs (ITCS 2013) rule out a large class of techniques to prove the security of correlation-secure hash functions in the standard model. Our construction is based on puncturable PRFs (Sahai und Waters; STOC 2014) and indistinguishability obfuscation. However, our proof also relies on point obfuscation under auxiliary inputs (AIPO). This is crucial in light of Wichs\' impossibility result. Namely, Wichs proves that it is often hard to reduce two-stage games (such as UCEs) to a \"one-stage assumption\" such as DDH. In contrast, AIPOs and their underlying assumptions are inherently two-stage and, thus, allow us to circumvent Wichs\' impossibility result.

Our positive result is also noteworthy insofar as Brzuska, Farshim and Mittelbach (Crypto 2014) have shown recently, that iO and some variants of UCEs are mutually exclusive. Our results, hence, validate some of the new UCE notions that emerged as a response to the iO-attack.

Participatory sensing enables new paradigms and markets for information collection based on the ubiquitous availability of smartphones, but also introduces privacy challenges for participating users and their data. In this work, we review existing security models for privacy-preserving participatory sensing and propose several improvements that are both of theoretical and practical significance.

We first address an important drawback of prior work, namely the lack of consideration of collusion attacks that are highly relevant for such multi-user settings. We explain why existing security models are insufficient and why previous protocols become insecure in the presence of colluding parties. We remedy this problem by providing new security and privacy definitions that guarantee meaningful forms of collusion resistance. We propose new collusion-resistant participatory sensing protocols satisfying our definitions: a generic construction that uses anonymous identity-based encryption (IBE) and its practical instantiation based on the Boneh-Franklin IBE scheme.

We then extend the functionality of participatory sensing by adding the ability to perform aggregation on the data submitted by the users, without sacrificing their privacy. We realize this through an additively-homomorphic IBE scheme which in turn is constructed by slightly modifying the Boneh-Franklin IBE scheme. From a practical point of view, the resulting scheme is suitable for calculations with small sensor readings/values such as temperature measurements, noise levels, or prices, which is sufficient for many applications of participatory sensing.

Password-based authentication schemes are convenient, but vulnerable to simple dictionary attacks. Cryptographic secret keys are safe, but difficult to memorize. More recently, biometric information has been used for authentication schemes. Das proposed a biometric-based authentication scheme, but it has various vulnerabilities. Jiping et al. improved Das\'s scheme, but some vulnerabilities remain. In this paper, we analyze the cryptanalysis of Jiping et al.\'s authentication scheme and propose the security enhanced biometric-based user authentication scheme for the C/S System.

We use various laws of classical physics to offer several solutions of Yao\'s millionaires\' problem without using any one-way functions. We also describe several informationally secure public key encryption protocols, i.e., protocols secure against passive computationally unbounded adversary. This introduces a new paradigm of decoy-based cryptography, as opposed to ``traditional\" complexity-based cryptography. In particular, our protocols do not employ any one-way functions.

Following the pioneering CRYPTO \'99 paper by Kocher et al., differential power analysis (DPA) was initially geared around low-cost computations performed using standard desktop equipment with minimal reliance on device-specific assumptions. In subsequent years, the scope was broadened by, e.g., making explicit use of (approximate) power models. An important practical incentive of so-doing is to reduce the data complexity of attacks, usually at the cost of increased computational complexity. It is this trade-off which we seek to explore in this paper. We draw together emerging ideas from several strands of the literature---high performance computing, post-side-channel global key enumeration, and effective combination of separate information sources---by way of advancing (non-profiled) `standard DPA\' towards a more realistic threat model in which trace acquisitions are scarce but adversaries are well resourced. Using our specially designed computing platform (including our parallel and scalable DPA implementation, which allows us to work efficiently with as many as 2^{32} key hypotheses), we demonstrate some dramatic improvements that are possible for `standard DPA\' when combining DPA outcomes for several intermediate targets. Unlike most previous `information combining\' attempts, we are able to evidence the fact that the improvements apply even when the exact trace locations of the relevant information (i.e. the `interesting points\') are not known a priori but must be searched simultaneously with the correct subkey.